Polymeric films

Abstract

Biaxially oriented polymeric films consisting of a first layer of a propylene homopolymer having on one side thereof and coextensive therewith a second layer of a non-voided propylene homopolymer and on the other side thereof and coextensive therewith a third layer of a voided propylene homopolymer, the said second layer having a heat sealable layer thereon and coextensive therewith. Films of the invention have puncture resistance combined with good gloss.

I claim: 
     
       1. A biaxially oriented puncture resistant polymeric film for heat sealing onto a substrate comprising a first layer of a propylene homopolymer having on one side thereof and coextensive therewith a second layer of a non-voided propylene homopolymer and on the other side thereof and coextensive therewith a third layer of a voided propylene homopolymer, said third layer including 14%-25% by weight of chalk as a voiding agent; the said second layer having a heat sealable layer thereon and coextensive therewith whereby said film is capable of providing evidence of tampering when said film is peeled from said substrate after said film has been heat sealed thereto. 
     
     
       2. A film according to claim 1, wherein the said first layer is non-voided. 
     
     
       3. A film according to claim 1, wherein the said first layer is voided. 
     
     
       4. A film according to claim 1, wherein the said first layer includes a pigment. 
     
     
       5. A film according to claim 1, wherein the said second layer includes a pigment. 
     
     
       6. A film according to claim 1, wherein the said third layer includes a pigment in addition to a particulate material which induces the voiding. 
     
     
       7. A film according to claim 4, wherein the pigment in one or more of said layers comprises titanium dioxide. 
     
     
       8. A film according to claim 1, wherein the said third layer has at least one polymeric layer coextensive therewith. 
     
     
       9. A film according to claim 6, wherein the said at least one polymeric layer includes an outer heat sealable layer. 
     
     
       10. A film according to claim 1, wherein at least the heat sealable layer on the said second layer and any heat sealable layer on the said third layer comprises a copolymer containing units derived from propylene and from at least one of ethylene and but-1-ene, or a linear low density polyethylene. 
     
     
       11. A film according to claim 1, wherein at least one of the outer surfaces of the film has been treated to increase its surface energy. 
     
     
       12. A biaxially oriented polymeric film comprising a core layer of a non-voided propylene homopolymer containing a pigmentary amount of titanium dioxide, a first intermediate layer on one side of the core layer said intermediate layer being of a non-voided propylene homopolymer and a second intermediate layer on the other surface of the core layer, the second intermediate layer being of a voided propylene homopolymer containing from about 14%-25% by weight of chalk as a voiding agent and a pigmentary mount of titanium dioxide, the film furthermore having two outer heat sealable layers. 
     
     
       13. A film according to claim 12, wherein the second intermediate layer contains about 20% by weight of chalk as the voiding agent. 
     
     
       14. A film according to claim 12, wherein the second intermediate layer contains about 5% by weight of titanium dioxide pigment. 
     
     
       15. A film according to claim 12, wherein the core layer contains about 2% by weight of titanium dioxide pigment. 
     
     
       16. A biaxially oriented polymeric film comprising a core layer of a voided propylene homopolymer containing a pigmentary mount of titanium dioxide, a first intermediate layer on one side of the core layer said intermediate layer being of a non-voided propylene homopolymer containing a pigmentary mount of titanium dioxide, and a second intermediate layer on the other surface of the core layer, the second intermediate layer being of a voided propylene homopolymer containing from about:14%-25% by weight of chalk as a voiding agent and a pigmentary amount of titanium dioxide, the film furthermore having two outer heat sealable layers. 
     
     
       17. A film according to claim 16, wherein the first intermediate layer contains about 10% by weight of titanium dioxide pigment. 
     
     
       18. A film according to claim 16, wherein the second intermediate layer contains about 14% by weight of chalk as a voiding agent. 
     
     
       19. A film according to claim 16, wherein the second intermediate layer contains about 5% by weight of titanium dioxide pigment. 
     
     
       20. A film according to claim 16, wherein the core layer contains about 5% by weight of chalk as a voiding agent.